chambers



Oct. 28, 1958 l. CHAMBERS 2,858,182

OSCILLOGRAPH APPARATUS Filed May 24, 1956 s Sheets-Sheet 1 FIG 2. I MV INVENTOR. HERBERT CHAMBERS A TTORNEYS Oct. 28, 1958 H. 1. CHAMBERS OSCILLOGRAPH APPARATUS 3 Sheets-Sheet 2 Filed May 24, 1956 INVENTOR. HERBERT l CHAMBERS A T TORNE VS Oct. 28, 1958 H. CHAMBERS 2,858,182

,OSCILLOGRAPH APPARATUS Filed May 24, 1956 3 Sheets-Sheet 3 IN VEN TOR. HERBERT CHAMBERS ATTORNE V S United States Patent Gfiflce Patented Oct. 28, 19,5 8

OSCILLOGRAPH APPARATUS Herbert I. Chambers, Pasadena, Calif., assignor to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Application May 24, M56, Serial No. 586,966

Claims. (Cl. 346-74) This invention relates to improvements in multichannel string galvanometers which record a plurality of oscillographic traces directly upon a recording medium such as current-sensitive paper.

In a typical string galvanometer, the writing element is a string, i. e., a movable conductor. The string is supported at its two ends so that its central portion can be deflected transversely a relatively large distance in either direction to provide the large amplitudes of motion which are required for recording directly.

The conductive string is located in a magnetic field perpendicular to the direction of the magnetic field, so that the string moves transversely with respect to the magnetic flux in accordance with the magnitude of the electric current which flows through it in response to an applied signal.

Preferably, the string is supported at each end by springs so that as the string is deflected in either direction, the springs permit the ends of the string to move closer together.

For direct writing on current-sensitive recording paper, an anvil having an edge located at the central portion of the string is employed to guide the recording paper adjacent the center of the string. The edge of the anvil is perpendicular to the string, and the current-sensitive paper is moved over the edge of the anvil so that it passes between the anvil and the string. Suitable means are provided for urging the string against the paper where the paper passes over the edge of the anvil, and a source of current is coupled between the paper and the string so that an electric current passes between the paper and the string at the intersection of the string and the line formed where the recording paper passes over the edge of the anvil. The current density at the point of contact between the paper and the string is sufliciently high to turn the paper black at that point. Thus, a trace is formed on the paper which provides a record of the deflections of the string in response to an applied signal.

In many types of measurements it is desirable to record the traces of two or more signals simultaneously on a common piece of current-sensitive recording paper. In such cases, a multi-channel oscillograph is used. Such a device employs as many strings as necessary to record the various signals. The strings are usually spaced side by side, parallel and in a common plane. Each string is adapted to travel over a separate given width or channel of the paper in recording its respective measurement.

One of the difliculties presented by multi-channel direct recording oscillographs using current-sensitive paper is that of obtaining satisfactory traces when signals of different frequencies are recorded simultaneously, because a relatively high voltage is required for satisfactory recording of a high frequency signal, while less voltage is necessary for a low frequency signal due to better contact between the paper and the slower moving string. The current-sensitive paper has a common electro-conductive surface, and, prior to this invention, the use of voltage suflicient to record a high frequency trace in one channel sometimes burned the paper in another channel being used to record a lower frequency.

This invention overcomes this difliculty by providing means for applying to the paper separate voltages adjacent each string to supply the amount of current required for proper recording in each channel.

Briefly, the invention contemplates a multi-channel oscillograph using a plurality of string galvanometers for direct recording in separate channels on current-sensitive paper. Means are provided for imposing between 'each channel and its respective string a voltage for proper recording of the trace generated by the string on the paper.

Preferably, each voltage is applied to each channel by a separate electrode adapted to make a sliding contact with the paper in its respective channel and adjacent the point of contact between the paper and the respective string.

The invention is explained in ence to the drawings, in which:

Fig. 1 is a fragmentary, partially schematic, elevation of one embodiment of the invention;

Fig. 2 is a sectional view along line 2-2 of Fig. 1;

Fig. 3 is a partially schematic view along line 3-3 of Fig. 1;

Fig. 4 is an enlarged detail plan view of a means for anchoring the ends of the string;

Fig. 5 is an elevation of the anchoring means of Fig. 4; and

Fig. 6 is a schematic fragmentary perspective view of an alternate arrangement of the anvil in which the anvil imposes the desired voltages on the channels of the paper.

For simplicity, the following detailed description is limited to a two-channel oscillograph, although the invention is applicable to oscillographs using any number of a plurality of channels.

Each string element (for simplicity, only one string is shown in Figs. 1 and 2) is a flexible conductor 10 which is supported at opposite ends by a pair of leaf springs 12. A conductive bearing sleeve 14 of ferromagnetic material is coaxially disposed around and soldered to the center of the string. The leaf springs are mounted at opposite ends of a base strip 16 which is made of a suitable nonmagnetic material, such as aluminum, and which is at tached by bolts 18 across a magnet yoke 20.

The magnet yoke supports an upper pole piece split into right and left (as viewed in Fig. 1) upper pole members 21, 22 respectively. The upper pole members are collinear and spaced apart. A writing anvil 24 is mounted between the upper pole members and has an elongated bottom edge 25 contoured to permit the smooth passage of a strip of current-sensitive recording paper 26 to pass over it between the pole pieces and in direct contact with the conductive bearing sleeve on the string. The paper moves from a supply reel 23 to a take-up reel 29 over guide rollers 30. The reels are powered by suitable means (not shown). The anvil edge is perpendicular to the string and extends for a distance sufficient to support the paper for as many channels as may be used. For example, as shown in Fig. 3 the lengthof the anvil covers the width of paper required for two channels.

A lower pole piece 32 is located directly below and spaced from the upper pole members. The string is dis posed in the space between the upper and lower pole members and is perpendicular to the flux between the upper and lower pole pieces, which are connected bythe yoke. The sleeve is magnetically attracted toward the anvil and maintains the proper writing pressure against the paper.

more detail with referof its ends.

A separate mounting bar 34 is attached by screws 35 near each end of the base strip and extends perpendicularly to the strip into the respective space between the magnet yoke and each side of the lower pole piece. Each bar is further secured to the yoke by a key 36 slip-fitted into a groove 37 in the side of the bar facing the yoke. The key is also press-fitted into a second groove 38 in the yoke and extends parallel to the mounting bar for almost the entire length of the bar. Thus, the entire string and leaf spring assembly may easily be slid from the yoke. A separate, externally threaded mounting pin 40 of electrical conductive material extends vertically (as viewed in Fig. 1) through each mounting bar, and is secured to the mounting bar by a nut 41 threaded into the lower end of the mounting pin. The pin in the right hand (Fig. 2) bar is near the end of the bar remote from the base strip, and the pin in the left hand bar is near the end of the bar adjacent the strip. A conductive sleeve 42 is disposed around the lower end of each pin and held up against the under side of the respective bar "by the respective nut on each pin. Electrical connection is made to each end of the flexible conductor by leads 44 soldered to the sleeves and connected to a signal source 45. The detail construction of the pins is best explained by reference to Figs. 4 and which show a mounting pin in detail. Each pin has a cylindrical head 48 with a slot 49 extending across a chord of the head near its center. A first raised four-sided boss 50 on the right hand (as viewed in Fig. 4) side of the head lies between the slot 49, a narrow groove 52 extending parallel to the slot, and a wider groove 53 extending inwardly from the periphery of the head to the edge of the slot. The groove 53 is perpendicular to the slot. The grooves 52 and 53 are not as deep in the head as is slot 49, which receives a screw driver during the mounting of the pin in the bar. Grooves 52 and 53 have bottom surfaces which are in a plane common to a level portion 54 of the head, which lies on the side of the slot opposite from grooves 52 and 53.

A second raised four-sided boss 56 is on the left hand side of the head between slot 49 and narrow groove 52. The left hand boss has a tapped horizontal bore 58 to receive a set screw 59. The left spring supporting the left end of the string is mounted in the pin shown in Fig. 4. An end 60 of the leaf spring is bent at right angles to the intermediate portion of the spring. The spring is bent at the opposite end 61 in a gradual curve to form a free end extending in the same direction as the end 60. Free end 61 is diminished in both width and thickness toward its tip to provide a free end with a small mass and the ability to vibrate in the frequency range required by the flexible conductor. End 60 of the leaf spring rests in groove 52 and is held in place in the groove by a wedge 62, which is kept in the groove by peening the edge of the groove as shown at 63. The intermediate portion of the leaf spring extends along the groove 53 and is held in a cantilever position over the flat portion 54 of the head by an L-shaped clamp 64 and set screw 59. One leg of the clamp lies in groove 52 where it is slidably retained by peening the edge of the groove at 65, and the other leg lies in wider groove 53.

The string has a flattened portion 66 adjacent each Flattened portion 66 at the left end of the conductor, as viewed in Fig. 5, extends along the convex surface of the leaf spring so that the major dimension of the flattened portion is vertical. The flattened portion is held between the L-shaped clamp and the intermediate portion of the leaf spring. A cylindrical tip 67 is left on the end of the conductor and acts as an index to position the conductor by contacting the curved portions of the L- shaped clamp and the leaf spring.

A similar arrangement at the opposite end of the conductor insures that the desired tension is imparted to the flexible conductor when the conductor is fastened to the springs. For instance, in Fig. 4, cantilever spring 12 assumes the free position shown by dotted lines 69. The

4 distortion of the spring under the full vibration amplitude of the conductor is indicated by dotted lines at 70.

The flattened portion of the conductor is in electrical contact with the mounting pin, and in mechanical contact with the leaf spring from the clamped spring end 60 to near its free end 61. Since the thickness of the conductor is reduced in the direction of conductor deflection, the conductor bends easily in this direction, while resisting bending in the direction normal to deflection. The vibration of the conductor causes the conductor to bend in that position nearest the free end of the leafspring. Since the leaf spring gives due to the added tension caused by deflection of the conductor, the point of tangency of the conductor to the curved free end of the spring changes and shifts the conductor bending point accordingly. Thus, the bending strain is distributed as the conductor vibrates and the condutcor is less susceptible to fatigue.

The right hand leaf spring is similarly mounted in the right hand pin so that its free end is cantilevered away from the pin and curves toward the left hand spring, and the right end of the flexible conductor is mounted on the right hand leaf spring as just described for the left end of the conductor. The pins are arranged on their respective mounting bars so that the leaf springs are on opposite sides of the flexible conductor as shown in Fig. 2;

When the flexible conductor is not subjected to current flow, it assumes a position midway between the full line position of conductor 10 and the dotted line position 10A in Fig. 2. In this unexcited position the bearing sleeve occupies a central position with respect to the lower pole piece. When current flows through the conductor, the bearing sleeve moves from side to side of a central line 71 as it vibrates from peak to peak of its oscillation. The displacement transverse to the direction of vibration is due to the mounting of the leaf springs on opposite sides of the conductor. This transverse motion tends to distribute the writing wear over the entire surface of the bearing sleeve and also keeps the surface of the bearing sleeve wiped clean.

The central lower pole piece is cut out as best shown in Fig. 2 so that the magnetic field in which the bearing sleeve moves increases as the amplitude of the conductor increases. This magnetic flux distribution helps to compensate for the non-linear eflects introduced by the fact that the amplitude induced by current flow varies inversely with the tension on the flexible conductor.

Referring to Fig. 3, a second conductor or string 72 is mounted adjacent the conductor 10 described with respect to Figs. 1 and 2. A conductor 72 is parallel to and laterally spaced from conductor 10 and is attached to each end in a manner identical to that described for conductor 10. Conductor 72 lies in a magnetic flux which is provided by an arrangement identical to that shown for conductor 10, and is adapted to slide over the recording paper as previously described for conductor 10.

Referring to Figs. 1 and 3, a first electrode 74 is mounted on the end of left hand pole piece by screws 76 and washers 77 made of suitable insulating material, such as plastic, which electrically insulate the electrode from the pole piece. The electrode has a plurality of parallel and laterally spaced contact fingers 78 which extend away from the screws 76 to terminate adjacent edge 25 of the anvil. The end of the fingers adjacent the anvil edge are curved away from the pole piece and extend toward the anvil and rest against the current-sensitive paper.

The first electrode is supplied voltage from a first writing current generator 79 through a potentiometer 80. The width of the first electrode is approximately equal to the amplitude through which the string 10 is normally expected to swing and defines a first channel 81 shown in dotted lines on the paper. Thus, the first electrode supplies a constant voltage to the paper over the full width of the first channel.

A second electrode 82, identical in construction to the first electrode, is laterally spaced from and mounted parallel to the first electrode by insulating screws 83 and insulating washers (not shown). The second electrode has fingers 84 which terminate on the paper adjacent the anvil edge and cover the amplitude over which the second string normally swings to define a second channel 85 shown in dotted lines on the current-sensitive recording paper.

A second writing current generator 86 supplies the second electrode voltage through a potentiometer 87.

The multi-furcated structure of the electrodes assures a large contact area of the electrodes against the recording paper and permits a lower current density flowing from the electrodes to the paper, thereby preventing marking of the paper at its points of contact with the electrodes. The fingers also permit the voltage to be applied to the paper as close to the contacts made by the respective strings as reasonable tolerance will allow.

The operation of the oscillograph is as follows:

Assume that the first string is to record a relatively high frequency signal, say 250 C. P. S., and that the second string 72 is to record a lower frequency, or even static D. C. The supply and take-up reels are started to move the recording paper over the edge of the anvil. The first potentiometer is set to apply a voltage to the first electrode which is higher than the voltage applied to the second electrode from the second potentiometer. With this arrangement, as the first string swings across channel 81 with a relatively high frequency, the higher voltage applied to the paper across channel 81 insures that an adequate current fiows between the string and the paper to make a proper trace. In the same manner, the lower voltage imposed by the second electrode on channel 85 of the paper insures that proper recording current flows between the paper and the second string.

Thus with this invention, although the adjacent strings may be recording signals of widely different frequencies, a uniform trace density is obtained by each channel.

Moreover, with the adjustable potentiometers each electrode can be supplied the proper voltage, depending on the frequency of the signal which its respective channel is to record.

Fig. 6 shows an alternate arrangement which is used when the recording paper is of such character as to conduct current in a direction perpendicular to its major surface, or when alternating writing current is used and the frequency is sufficiently high to cause the paper to be marked even though the paper ordinarily does not conduct current perpendicularly to its major surface. An anvil 90 is formed with conducting portions 91, 92 at each end. The central portion 93 of the anvil is an electric insulator. Conducting portions 91, 92 are respectively connected by leads 94, 95 to potentiometers 96, 97 which permit the opposite ends of the anvil to be independently supplied adjustable amounts of current and voltage. Separate conductors or strings 98, 99 are supported as described above to extend perpendicularly over an edge of the anvil, and a strip of recording paper (shown in phantom lines) is arranged to pass between the strings and the anvil, as described above.

With the arrangement of Fig. 6, each conductive portion of the anvil spans a channel on the paper and maintains the desired voltage for its respective channel, thereby eliminating the need for electrodes on the same side of the paper as the string. This permits minimum spacing between the point at which voltage is applied to the paper and the point of contact between the string and the paper, and further improve the control of the recording current supplied to the separate channels.

I claim:

1. An oscillograph for direct recording of at least two traces on a common recording medium with independent writing voltages comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the 6 magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, and means for imposing different voltages between the first conductor and the portion of the paper adjacent the first conductor, and between the second conductor and the portion of the paper adjacent the second conductor.

2. An oscillograph for direct recording of at least two traces on a common recording medium with independent v/riting voltages comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, means for imposing one voltage between the first conductor and the portion of the paper adjacent the first conductor, and means for imposing a different voltage between the second conductor and the portion of the paper adjacent the second conductor.

3. An oscillograph for direct recording of at least two traces on a common recording medium with independent writing voltages comprising means for producing a magnetic field, a first movable conductor adapted to receive a first signal at one frequency, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor and adapted to receive a second signal at a frequency lower than the frequency of the first signal, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, means for imposing a higher voltage between the first conductor and the portion of the paper adjacent the first conductor than between the second conductor and the portion of the paper adjacent the second conductor.

4. Apparatus according to claim 3 in which the means for imposing the voltage is an electrode in contact with the paper adjacent the first conductor.

5. Apparatus according to claim 4 in which the electrode has a plurality of fingers contacting the paper.

6. Apparatus according to claim 4 in which the first conductor oscillates on the paper in response to the first signal with a maximum amplitude, and in which the electrode contacts the paper for a distance equal to the maximum amplitude of the oscillation of the first conductor.

7. An oscillograph for direct recording of at least two traces on a common recording medium with independent writing voltages comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, a first electrode in contact with the paper adjacent the first conductor for imposing one voltage between the first conductor and the portion of the paper adjacent the first conductor, and a second electrode in contact with the paper adjacent the second conductor for imposing a difierent voltage between the second conductor and the portion of the paper adjacent the second conductor.

8. An oscillograph for direct recording of at least two traces on a common recording medium with independent writing voltages comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, a first electrode in contact with the paper on the same side of the paper as the conductors and adjacent the first conductor for imposing one voltage between the first conductor and the portion of the paper adjacent the first conductor, and a second electrode in contact with the paper on the same side of the paper as the conductors and adjacent the second conductor for imposing a difierent voltage between the second conductor and the portion of the paper adjacent the second conductor.

9. An oscillograph for direct recording of at least two traces on a common recording medium with independent writing voltages comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the anvil and on the other side by the conductors, a first electrode in contact with the paper on the same side of the paper as the conductors and adjacent the first conductor for imposing one voltage between the first conductor and the portion of the paper adjacent the first conductor, a second electrode in contact with the paper on the same side of the paper as the conductors and adjacent the second conductor for imposing a different voltage between the second conductor and the portion of the paper adjacent the second conductor, and means for adjusting the voltages applied by the electrodes.

10. An oscillograph for direct recording of at least two traces on a common recording medium with inde pendent writing voltages comprising means for producing a magnetic field, a first movable conductor, means for supporting the first conductor in the magnetic field with the first conductor extending transverse to the direction of the magnetic field, a second movable conductor spaced from the first conductor, means for supporting the second conductor in the magnetic field with the second conductor extending transverse to the direction of the magnetic field, an anvil located adjacent and extending transverse to the conductors, the anvil having two electrically conductive portions insulated from each other, current-sensitive paper located between the anvil and the conductors, means for urging the conductors toward the anvil so that the paper is contacted on one side by the conductive portions of the anvil and on the other side by the conductors, means for imposing one voltage on one of the conductive portions of the anvil, and means for imposing a different voltage on the other conductive portion of the anvil.

No references cited. 

